1. Field of the Invention
The present invention relates to a brushless DC motor used as a driving source for a moveable vane of a VG Variable Geometric) turbo system, an EGR (exhaust gas recirculation system) valve or a throttle valve used in on-vehicle equipment.
2. Description of Related Art
A conventional brushless DC motor, as disclosed for example in JP-A-11-346497, is constituted by a rotor which retains a permanent magnet having magnetic poles on an outer periphery, a bearing portion which rotatably supports the rotor, a stator with current-carrying coils wound thereon which is disposed on an outer side of the rotor, a rotation position detection means which switches the power supply to the plurality of coils retained on the stator in accordance with the position of the rotor, a housing which stores the above components, and a control circuit for controlling the drive operation of the motor.
The structure of a general brushless DC motor similar to the above motor will be described with reference to FIG. 7.
In the figure, reference numeral 1 denotes a permanent magnet, 2 is an output shaft, and 3 is a rotor. The permanent magnet 1 which is magnetized with a fixed number of magnetic poles is mounted on the outer periphery of the output shaft 2. 4 denotes a bearing which rotatably supports both end portions of the rotor 3. 5 is a core which faces with the outer peripheral face of the permanent magnet 1 disposed on the outer periphery of the rotor 3. 6 is a coil wound on the core 5 for generating an electromagnetic force in the core 5 by the application of a current. 7 is a housing which supports the outer periphery of the core 5. 8 is a stator which is constituted by the core 5 and the coils 6 and which is fixed in the housing 7. 9 is a Hall device which is arranged in proximity to one axial end face of the permanent magnet 1 disposed on the outer periphery of the rotor 3. The Hall device 9 detects the rotation position of the rotor 3 by sensing the leakage flux in an axial direction of the permanent magnet 1. 10 is a base plate which supports the Hall device 9 in proximity to the axial end face of the permanent magnet 1. 11 is a threaded section for fixing the base plate 10 on the housing 7. 12 is a motor section containing all the above constituent elements.
13 is a control circuit section for driving the motor section 12, and the control circuit section 13 is normally provided in a separate position to the motor section 12. 14 is a harness for placing the motor section 12 and the control circuit section 13 in electrical connection.
In the conventional brushless DC motor constituted as above, the rotational angular position of the rotor 3 is detected by a plurality of Hall devices, the current applied to each coil 6 arranged in three-phase is switched in response to the output signal. As a result, attractive and repulsive forces alternate with respect to each pole of the permanent magnet 1 on the rotor 3 and results in the generation of a rotation torque in the rotor 3.
Further, in the conventional brushless DC motor constituted as above, the Hall device is frequently used as a position detection means for the rotor, which detects the leakage magnetic flux from the permanent magnet of the rotor and to convert it into an electrical signal. Thus, it is necessary to dispose the Hall device in a position adjacent to the axial end face of the permanent magnet provided in the rotor. The precise position is shown in FIG. 11 of the publication JP-A-11-346497 in which it is necessary to arrange the Hall devices on the inner side of the bearing members supporting the rotor.
The control circuit section which switches the power supply to the coils in accordance with the positional signal must be disposed in a separate position to the motor due to problems related to the heat resistance characteristics of the electronic components, and thus, the motor and the control circuit section are electrically connected by a harness.
Since the conventional brushless DC motor is constituted as above, a harness must be provided in order to electrically connect the motor with the control circuit section when the motor and the control circuit section are provided separately. Furthermore, a motor, a casing member for each control circuit section and a seal or similar component for the harness extraction section from the casing member are required. This structure is not only expensive but in addition requires a housing for storing the control circuit section and additional space for arranging the housing.
In order to integrate the motor and the control circuit section, the control circuit section must be mounted on the base plate for the Hall device which is disposed in proximity to the permanent magnet on the rotor. However, the problem of heat damage on the control circuit section due to heat generated by the coils is not avoided.
Further, when the control circuit section is mounted on an another base plate than the base plate for the Hall device and is integrated with a motor, it is necessary to electrically connect the base plate for the Hall device and the base plate for the control circuit section with a harness or the like. As a result, structural complexity is increased, freedom of design with respect to component shape is limited and manufacturing costs increase.
Furthermore, since large temperature variations result from generation of heat by the coils in a tightly-closed motor, it is sometimes the case that a breathing phenomenon is generated due to a pressure difference between the atmospheric pressure and the pressure in the motor. For example, when moisture enters into the motor as a result of the breathing, the possibility exists that short circuits or insulation failure may result from the moisture entering into the control circuit section.
The present invention is proposed to solve the above problems and has the object of providing a brushless DC motor with simplified and cost-effective structure of circuit connection section, in which the control circuit section is integrally mounted in a position not affected by heat generation from the coils.
According to the present invention, there is provided a brushless DC motor comprising: a motor section having a rotor, a stator and a housing; a control circuit section which is integrated with the motor section and which is partitioned from the motor section; and a casing member for isolating the control circuit section from the external environment, wherein a position detection means is disposed outside of a bearing member with respect to the axial direction.
Here, according to the present invention, the partition may be formed by at least one of the housing constituting the motor section and the casing member covering the control circuit section.
According to the present invention, the partition may be formed with a resinous material.
According to the present invention, the partition may be formed by the casing member covering the control circuit section, and the casing member may be formed with a resinous material.
According to the present invention, the power source and the connector for signal input may be provided integrally with the casing member.
According to the present invention, the coils may be electrically connected with the control circuit section by a connection terminal which passes through the partition, and the partition through-hole for the connection terminal may be sealed by a seal member.
According to the present invention, the fitting portion of the housing and the casing member may be adapted to have at least one of a waterproofing function and a dustproofing function.
According to the present invention, a seal member may be provided in the fitting portion of the housing and the casing member.
According to the present invention, the housing and the casing member may be formed with a resinous material, the housing and the casing member may be joined by partially or completely fusing the fitting portion of the housing and the casing member.
According to the present invention, the position detection means may function by magnetic detection.
According to the present invention, the position detection means may be provided with a permanent magnet and a Hall device.
According to the present invention, the magnet for the position detection means may be provided as a second permanent magnet which is a separate component from the first permanent magnet.
According to the present invention, the partition may be arranged between the second permanent magnet and the Hall devices.
According to the present invention, the second permanent magnet may be formed with a plastic magnet.
According to the present invention, the second permanent magnet may be adapted to rotate together with the rotor.
According to the present invention, the rotor and the second permanent magnet may be integrally fixed by plastic deformation of at least one of them.
According to the present invention, the rotor and the second permanent magnet may be integrally fixed by thermal deformation of at least one of them.
According to the present invention, a positioning member for determining the magnetic pole positions of the second permanent magnet may be arranged between the rotor and the second permanent magnet.
According to the present invention, the positioning member may be constituted by a projection provided on one of the rotor and the second permanent magnet and a notch provided on the other of the rotor and the second permanent magnet, the positioning member positioning the second permanent magnet by meshing the projection with the notch.
According to the present invention, the positioning member may be a locating pin.
According to the present invention, the Hall devices may be disposed opposite to the position at which the second permanent magnet generates a maximum magnetic flux.
According to the present invention, the number of magnetic poles in the second permanent magnet may be twice the number of magnetic poles in the first permanent magnet.